Possible to put main ducts between joists?

[swampwiz]

I've got a rather tricky situation. The unit will be in the attic, but the duct work (intake and outtake) must go to the angle of the attic. That in and of itself is not a problem, but the only walkable area is between the duct and the unit, and the duct work cannot simply lie on the floor (as there would not be enough height for attic egress.) The only solution seems to be to run the ducts along the joists.

The 2x10 joists will be at the standard 16" spacing. It seems that the ducts could run along these joists in a series of 9" x 14" rectangular ducts (126 in^2 each.) There is room for 4 rows of ducts (2 intake, 2 outtake.) Since the whole space of the home will be insulated (spray foam insulation), it seems that there would not need to be any insulation on the ducts.

My question is whether this will be enough cross section area for the system. The structure will probably get a 4-1/2 ton unit for a 2900 ft^2 ground floor home (that will be excellently insulated.)

Also, I figure that some folks before me have done this as well, so there must be some standard cross sectional stiff ducts that match the standard 16" joists for the various sizes of lumber (in this case, 2x10.) Is this an accurate assessment?

[beenthere]

Also, I figure that some folks before me have done this as well, so there must be some standard cross sectional stiff ducts that match the standard 16" joists for the various sizes of lumber (in this case, 2x10.) Is this an accurate assessment?

Nope.

Consult with your contractor.
He will be able to tell you what he can and can't do.

This is not DIY site.

[dash]

No standard or rule of thumb,just use Manual D, from www.acca.org ,the industy and ANSI standard, to have your ducts designed correctly the first time.

[HeyBob]

Nope.

Consult with your contractor.
He will be able to tell you what he can and can't do.

This is not DIY site.

Someone will do it, like those guys that bend under the pressure of getting the job from the builder that wants them run through the trusses in a basement. Those are nasty duct systems that don't work properly.

[beenthere]

If he's lucky. He won't find one of those companies. :D

[HeyBob]

If he's lucky. He won't find one of those companies. :D


Dime a dozen these days, side jobbers coming out of the woodwork in these parts!

[beenthere]

Plenty of side jobbers here too.

Just hard to find any that goofy. LOL

[HeyBob]

Plenty of side jobbers here too.

Just hard to find any that goofy. LOL


Not in these parts, a lot of contractors will squeeze an entire duct system into those holes in basement trusses and call it good...............hacked together crap. :D

[qwerty hvac]

Get your system designed by a good HVAC tech/company. And also make sure the ducts are insulated. It will save you money in the long run and help your system run more efficiently in an unconditioned attic. :cool:

[t527ed]

if he can find you a 4 1/2 ton unit he can make those ducts fit whatever he wants.........;):rolleyes::rolleyes:

[mchild]

I've got a rather tricky situation. The unit will be in the attic, but the duct work (intake and outtake) must go to the angle of the attic. That in and of itself is not a problem, but the only walkable area is between the duct and the unit, and the duct work cannot simply lie on the floor (as there would not be enough height for attic egress.) The only solution seems to be to run the ducts along the joists.

The 2x10 joists will be at the standard 16" spacing. It seems that the ducts could run along these joists in a series of 9" x 14" rectangular ducts (126 in^2 each.) There is room for 4 rows of ducts (2 intake, 2 outtake.) Since the whole space of the home will be insulated (spray foam insulation), it seems that there would not need to be any insulation on the ducts.

My question is whether this will be enough cross section area for the system. The structure will probably get a 4-1/2 ton unit for a 2900 ft^2 ground floor home (that will be excellently insulated.)

Also, I figure that some folks before me have done this as well, so there must be some standard cross sectional stiff ducts that match the standard 16" joists for the various sizes of lumber (in this case, 2x10.) Is this an accurate assessment?

Since it does not seem like you have yet begun working with any professionals on this, where did the 4.5 ton unit sizing come from? Where are you located? What is the heat gain and loss of this 2,900 sf foam insulated structure?

[paul42]

The duct work should be insulated. Even if the attic is inside the insulated space, you run the risk of condensation dripping onto your ceiling.

With multiple ducts, you might be able to fit them between the joists, it ain't going to be easy or pretty. Maybe change the design of the house to include a drop down ceiling in a hallway to run duct work.

4-1/2 tons seems way too large for a properly designed foam insulated 2,900 sq. ft. house - speaking from experience.